Plastic cups have been manufactured in a mold with a threaded mouth for mating engagement with a threaded cap. It is also known to manufacture in a separately constructed mold a plastic cup having a circumferential lip or tab around the mouth for mating engagement with a plastic snap-on cap. In order to create these two differently closed cups, it has been necessary to create two different molds, each of which are quite expensive to fabricate. Further, in order to quickly satisfy orders for both types of cups, it has been necessary to maintain large inventories of each of the different types of cups, since it would not be known when a large order for one or the other type cup would be made.
It has also been known that plastic cups may be formed with an outward taper toward the top to allow identical cups to be nested at least partially one within the other to reduce the space required during warehousing and shipping and to provide a convenient stack of cups at the point of use. It has been a problem with such nested cups that an air seal may develop between the touching surfaces of adjacently stacked cups such that a reduced air pressure is created within the cup as it begins to be removed from the adjacent cup. This reduced air pressure causes adjacent cups to stick together making separation and removal of a cup from the stack difficult and inconvenient. This problem is especially significant in a fast moving vending situation such as in a fast food establishment or an amusement park or fair grounds vending booth. That is to say, vendors in such places want cups that do not stick together so that peak customer demands can be accomodated without interruption and delay. Pressure differentials also may exist when the air between stacked cups is chilled after nesting, again creating difficulty in separating stacked cups.